Construction of 3,6-Anhydrohexosides via Intramolecular Cyclization of Triflates and Its Application to the Synthesis of Natural Product Isolated from Leaves of Sauropus rostratus

Abstract

A novel synthetic approach to construct various 3,6-anhydrohexosides via an intramolecular cyclization of corresponding triflates is described. The nucleophilic attack from C3 p-methoxybenzylated hydroxyl to C6 trifluoromethanesulfonate on triflate structures triggered the cyclization reaction to provide 3,6-anhydrohexosides in excellent yields, making the strategy more efficient with respect to the reported protocols. By applying this methodology, a concise first total synthesis of natural product isolated from leaves of Sauropus rostratus was accomplished.

Debenzylative Cycloetherification: An Overlooked Key Strategy for Complex Tetrahydrofuran Synthesis

“…Recently, the first total synthesis of natural product 143 , a potential anti‐inflammatory agent extracted from the leaves of Sauropus rotratus , was performed by Wu and co‐workers (Scheme ) . Interestingly, the DBCE reaction was used as a key step for this total synthesis in the presence of triflic anhydride and 2,6‐lutidine.…”

“…Indeed, the triflation of pyranosides 117 – 122 or furanosides 123 – 124 efficiently afforded [3.2.1] and [3.2.0] bicyclic structures in high yields. The DBCE was not affected by the nature of the other protecting groups (Scheme ) …”

Practical Route to Neokotalanol and Its Natural Analogues: Sulfonium Sugars with Antidiabetic Activities

“…[14] The 1 HNMR spectrum showed three benzyl groups as well as acetonide protection of the structure.T he 13 CNMR spectrum showed two peaks at d = 36.0 and 33.5 ppm corresponding to two vicinal carbon centers connected to at hiol ether rather than sulfoinum cation structure.I nterestingly,w hen kept in the CDCl 3 solution, the transformation from 14 into 15 a,a lbeit in trace amounts,w as detected. [14] The 1 HNMR spectrum showed three benzyl groups as well as acetonide protection of the structure.T he 13 CNMR spectrum showed two peaks at d = 36.0 and 33.5 ppm corresponding to two vicinal carbon centers connected to at hiol ether rather than sulfoinum cation structure.I nterestingly,w hen kept in the CDCl 3 solution, the transformation from 14 into 15 a,a lbeit in trace amounts,w as detected.…”

The Construction of Anhydro Monosaccharides

“…3,6‐Anhydrohexoside bearing the 2,6‐dioxabicyclo [3.2.1] octane structure is probably one of the most important anhydro sugars owing to its extensive presence in a number of bioactive natural products and synthetic molecules such as agarose ( 1 ), Kappa (κ)‐ and Iota (ι)‐carrageenan ( 2 ) and ( 3 ), Furanodictines A ( 4 ) and B ( 5 ), and staurosporine analogs ( 7 ). Recently, our group accomplished the first total synthesis of a 3,6‐anhydro hexofuranoside derivative ( 8 ) isolated from the leaves of Sauropus rostratus . In these compounds, the 3,6‐anhydrohexoside moiety acts as either a key structural motif to endow bioactive properties or an effective structural unit for physical property alteration.…”

“…Surprisingly, the coupling reaction only processed through route b, with the desired sulfonium salt being obtained in 84 % . On the other hand, the formation of 3,6‐anhydro mannopyranoside derivative 151 , albeit in poor yield, inspired us to carry out further investigations to develop a new strategy for the efficient construction of 3,6‐anhydro hexoside structures . First, a model substrate 154 was used to initiate our investigation.…”